There is no any information on the sources of \(^7\) Be(\(n\) ,\(\alpha \) )\(^4\) He cross-section data used in the Wagoner's original paper [1]}. Before his
estimation, there was only one measurement made by Bassi et al. [2]} at thermal neutron energy. Here, we have figured out the Wagoner's way of thinking.
The total cross section of \(^7\) Be(\(n\) ,\(\alpha \) )\(^4\) He was assumed to be composed of two contributions, i.e., \(\sigma _1\) +\(\sigma _2\) , with \(\sigma _1\)  for
the \(p\) -wave capture of (\(n\) ,\(\alpha \) ) and \(\sigma _2\)  for the \(s\) -wave capture of (\(n\) ,\(\gamma \alpha \) ), respectively. The former obeys the law of
\(\sigma _2\)\(\propto \)\(v\) , and the latter obeys the law of \(\sigma _1\)\(\propto \)\(1/v\)  [3]}, [4]}. According to this way, Wagoner made his estimation
based on an upper limit of \(\sigma _1\)\(\le \) 0.1 mb and \(\sigma _2\) =155 mb measured by Bassi et al. at thermal neutron energy. Actually, the \(p\) -wave dominates the
cross section (or total rate) at the energy region of BBN relevant. Therefore, Wagoner actually gave us only an upper limit.
